Wide area radio network systems of cellular type are well-known systems for solving communication problems. An example of such a system used in mobile applications is NMT (Nordic Mobile Telephone system) and GSM (Global System for Mobile communications). For fixed applications SR100 (Subscriber Radio) and SR500 from the Canadian Company (SR Telecom) can be mentioned.
In the systems mentioned, frequencies in adjacent or overlapping service areas that are served by the systems are used to prevent interferences between stations from occurring. This means that it is not possible to achieve redundancy in the system on common frequency bands in the different service areas which otherwise would be the most frequency efficient, and economic solution. There are also problems in expanding said systems with reference to capacity and area covering without a deterioration of the frequency efficiency.
Radio network systems comprise one or several central stations (CS) and a plurality of peripheral stations (PS) connected thereto. If a high security and an efficient redundancy, or recoupling ability between different CS operating within the same or any adjacent service area, should be obtainable within the framework of previously known technique said stations must be capable of operating on different frequencies so as to avoid interference. This leads to unnecessarily complicated and expensive stations. The construction and function of a CS in existing systems with respect to control functions is very fixed and no flexibility is allowed.